This invention relates to fuser heating apparatus and, in particular, to apparatus to produce uniform irradiance in a fusing cavity.
Many forms of image fusing techniques are known in the prior art such vapor fusing, heat fusing, pressure fusing or a combination thereof. Each of these techniques suffer from deficiencies which make their use impractical or difficult for specific xerographic applications, such as in reproducing apparatus capable of producing copies at an extremely rapid rate. Radiant flash fusing is one practical method of image fixing that lends itself to use in a high speed automatic process. The main advantage of the flash fuser over the other known methods is that energy, which is propagated in the form of electro-magnetic waves, is instantaneously available and requires no intervening medium for its propagation. It does not require long warm-up periods nor does the energy have to be transferred through a relatively slow conductive or convective heat transfer mechanism.
A major problem with flash fusing, however, in the xerographic fixing art has been designing apparatus which can fully and efficiently use a preponderance of the radiant energy emitted by the source during the relatively short flash period. In flash fusing, it is especially important to maintain a very uniform output across the entire flash cavity. To minimize power supply size, energy output should be set just slightly above the minimum fuse temperature. Minimal fluctuations in space in the energy output can easily result in under fusing parts of a copy and thereby require excess energy input to insure uniformity of fusing across the entire copy.
U.S. Pat. No. 3,529,129, commonly assigned, discloses a method to fix an electroscopic image to a final support material in which the image bearing support material is placed within an integrating cavity and exposed to radiation emitting from a flash lamp. The cavity wall, the flash lamp, and the support material are positioned in relation to each other such that the electroscopic powder is fixed sufficiently and uniformly. The radiant energy source and the image bearing support material to be fixed are placed within the reflective cavity which is constructed to functionally approximate an integrating sphere. A difficulty with this system is that it is relatively complex and is not easily adapted to fuser cavities that are relatively narrow or shallow.
It is an object of the present invention, therefore, to provide a new and improved flash fusing reflector cavity. It is another object of the present invention to provide a relatively shallow fuser reflector cavity having a combination of specular and diffuse reflecting surfaces to provide uniform irradiation with a minimum of power.
Further advantages of the present invention will become apparent as the following description proceeds, and the features characterizing the invention will be pointed out with particularity in the claim annexed to and forming a part of this specification.
The present invention is a fuser having an illuminating means disposed within a relatively narrow box-like cavity, the cavity including a plurality of reflecting surfaces to produce substantially uniform radiation across the cavity, the reflecting surfaces including a combination of diffuse and specular surfaces, in particular, a flat diffuse reflector, an essentially parabolic diffuse reflector, an a specular reflector disposed at one end of the parabolic diffuse reflector.